In your xinetd's tunnel-smtp configuration you have xinetd listen on 2525/tcp and in turn you want to build a tunnel using the same port, hence, listening on the very same port 2525 - this will not work. Since you seem to have more access to the SMTP server you try to connect to you could add the following in front of the corresponding line in authorized_keys:

I don't get any output or log from xinetd. And with 'no ssh login found' I mean that there is no entry about an incoming ssh connection at the server. So it looks like xinetd isn't firing up the tunnel correctly_________________Please stand by - The mailer daemon is busy burning your messages in hell...